Sole structure for electrostatic dissipative footwear and method of making same

ABSTRACT

An electrostatic circuit for a sole having an outsole, an insole and a midsole positioned between the insole and outsole. In one embodiment, the electrostatic circuit includes at least one conductor path that is printed on a first side of a first substrate. The conductor path may have a first exposed end attachable to the outsole and a second exposed end attachable to the insole. The electrostatic circuit may also include at least one resistor electrically that is coupled to each conductor path and mounted to the first substrate. In another embodiment, the electrostatic circuit may include first and second conductive pads attached to the first and second ends of each conductor path.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of U.S. patentapplication Ser. No. 09/844,798, filed Apr. 27, 2001 which is acontinuation-in-part application of U.S. patent application Ser. No.09/814,085, filed Mar. 21, 2001, entitled Sole Structure ForElectrostatic Dissipative Footwear and Method of Making Same, nowabandoned.

FEDERALLY SPONSORED RESEARCH

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The invention relates to footwear and, more particularly, tofootwear constructed to dissipate electrostatic charges.

[0005] 2. Description of the Invention Background

[0006] Static electricity is the accumulation of electric charge in aninsulated body, most frequently caused by friction, but also by othermeans, such as induction etc. Electrostatic discharge (ESD) is thetransfer of electric charge between two bodies, often accompanied by avisible spark, as in the familiar phenomenon of doorknob shock. Whileelectrostatic discharge per se may not be immediately harmful to a humanbody, at least at level of voltage less than about 3000 volts, adischarge of much smaller voltage might be damaging to sensitiveequipment, such as electronic components for computers and magnetic datacarriers. A low volt electrostatic discharge may also ignite explosivegases. Accordingly, protection against ESD is required in theelectronics and telecommunications industries and in other industrieswherein sensitive electrical components or explosive materials are beinghandled.

[0007] ESD is of particular concern to the electronics industries. Forexample, if a quality control inspector carries a static charge duringan inspection or testing operation, at a minimum, the accuracy of thetest may be affected or, in worse cases, one or more sensitivecomponents may be damaged. One method commonly employed to address thisproblem is the use of conductive footwear. By wearing a pair ofconductive shoes, the person testing the electronic products iselectrically grounded and the static charge is therefore eliminated.Various tests have shown that conductivity, more specifically, theimpedance of a conductive shoe must be maintained within a certainrange. One company in the computer and electronics industry recommendsthat the impedance of a conductive shoe be maintained within 10⁶ ohms to10⁷ ohms. Other forms of grounding have been used to dissipate theelectrostatic charge before it builds up to harmful levels. Suchgrounding measures include installing conductive or dissipative floorsor stepping mats and/or wearing conductive wrist straps.

[0008] The efficacy of antistatic devices such as footwear, wrist andheel straps, etc. is typically determined by the electrical resistanceof the conducting surface of the device in ohms. This electricalresistance may be affected by various environmental factors, such ashumidity, dirt and other contamination, wear and other damage. Avariable or unreliable electrical resistance does not provide continuousand reliable protection, as required in many environments withcomponents sensitive to relatively small electrostatic discharges.

[0009] There remains, therefore, a need for footwear with improvedelectrostatic discharge properties that overcomes the limitations,shortcomings and disadvantages of the previous approaches.

SUMMARY OF THE INVENTION

[0010] The invention meets the identified needs, as well as other needs,as will be more fully understood following a review of thisspecification and drawings.

[0011] One embodiment of the invention comprises an electrostaticcircuit for a sole having a conductive outsole, a conductive insole anda nonconductive midsole positioned between the insole and outsole. Thisembodiment of the electrostatic circuit includes a first substrate thathas a first end and a second end. In one embodiment, the substrate isflexible and in another embodiment, the substrate may be relativelyrigid and inflexible. The electrostatic circuit may further include atleast one conductor path that is attached to the first substrate. Eachconductor path has a first exposed end that is adjacent to the first endof the first substrate and that is attachable to the conductive outsole.Each conductor path also has a second exposed end that is adjacent tothe second end of the substrate and that is attachable to the conductiveinsole. In addition, the circuit includes at least one resistor that iselectrically coupled to each conductor path and mounted to the firstsubstrate. In alternative embodiments, each end of the conductive pathsmay be attached to a corresponding conductive pad to provide an enlargedarea for affixing the conductive path to the other components of thesole.

[0012] Another embodiment of the present invention includes anelectrostatic circuit for a sole that has a conductive outsole, aconductive insole and a nonconductive midsole between the insole andoutsole. In this embodiment, the electrostatic circuit includes a firstsubstrate that has a first end and a second end. A first conductor pathis attached to the first substrate. The first conductor path has a firstexposed end that is adjacent to the first end of the first substrate andthat is attachable to the conductive outsole. The first conductor pathalso has a second exposed end that is adjacent to the second end of thefirst substrate and that is attachable to the conductive insole. A firstresistor is supported on the first substrate and is electrically coupledto the first conductor path. In addition, a second conductor path isattached to the first substrate. The second conductor path has a secondexposed end that is adjacent to the first end of the first substrate andthat is attachable to the conductive outsole. The second conductor pathalso has a second exposed end that is adjacent to the second end of thefirst substrate and that is attachable to the conductive insole. Asecond resistor is supported on the first substrate and is electricallycoupled to the second conductor path. A third conductor path is attachedto the first substrate. The third conductor path has a first exposed endthat is adjacent to the first end of the first substrate and isattachable to the conductive outsole. The third conductive path also hasa second exposed end that is adjacent to the second end of the substrateand that is attachable to the conductive insole. A third resistor issupported on the first substrate and is electrically coupled to thethird conductor path.

[0013] Another embodiment of the present invention comprises a sole fora conductive shoe. The sole includes a conductive outsole and a midsolethat is adjacent to the outsole. A conductive insole is adjacent to themidsole. The sole further includes a printed circuit that comprises afirst substrate and at least one conductor path that is attached to thefirst substrate. Each conductor path has a first end that is attached tothe conductive outsole and a second end that is attached to theconductive insole. At least one resistor is electrically coupled to eachconductor path and mounted to the first substrate.

[0014] Yet another embodiment of the present invention comprises amethod for applying a desired amount of electrical impendence to anelectrostatic current passing through a shoe having a conductiveoutsole, a conductive insole and a nonconductive midsole between theoutsole and insole. The method includes affixing one end of a firstconductive path formed on a substrate to the conductive outsole andelectrically coupling a first resistor having the desired amount ofimpedance to the conductive path. The method further includes affixinganother end of the first conductive path to the conductive insole.

[0015] Another embodiment of the present invention comprises a method ofmanufacturing a sole for a conductive shoe. The method includes affixinga first conductive path to a substrate such that the first conductivepath has a first exposed end and a second exposed end and attaching afirst resistor to the first conductive path. The method also includesforming a conductive outsole and a nonelectrically conductive midsoleand supporting the nonelectrically conductive midsole on theelectrically conductive outsole. The method further includes forming anelectrically conductive insole and supporting the electricallyconductive insole to the nonelectrically conductive midsole. Thesubstrate is supported within the midsole such that the first exposedend of the first conductive path is in electrical contact with theelectrically conductive outsole and the second end of the firstelectrically conductive path is in electrical contact with theelectrically conductive insole.

[0016] Other features and advantages of the invention will becomeapparent from the detailed description of the embodiments set forthherein and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the accompanying Figures, there are shown present embodimentsof the invention wherein like reference numerals are employed todesignate like parts and wherein:

[0018]FIG. 1 is a side elevational view of an item of footwear with anembodiment of a sole of the present invention with portions of the soleshown in cross-section;

[0019]FIG. 2 is an enlarged partial view of the sole of FIG. 1 showingan orientation of one embodiment of a printed circuit of the presentinvention;

[0020]FIG. 3 is a cross-sectional assembly view of the sole of FIG. 1;

[0021]FIG. 4 is a top view of a midsole and a portion of a printedcircuit of the present invention;

[0022]FIG. 5 is a top view of an embodiment of a printed circuit of thepresent invention;

[0023]FIG. 6 is a side elevational view of conductive paths of theprinted circuit of FIG. 5;

[0024]FIG. 7 is a bottom view of the printed circuit of FIG. 5;

[0025]FIG. 8 is another top view of the printed circuit of FIG. 5, witha moisture barrier applied thereto;

[0026]FIG. 9 is a cross-sectional exploded assembly view of the printedcircuit of FIG. 8 taken along line IX-IX in FIG. 8;

[0027]FIG. 10 is an enlarged partial view of another sole embodimentshowing an orientation of another printed circuit of the presentinvention;

[0028]FIG. 11 is top view of a midsole and a portion of the printedcircuit depicted in FIG. 10;

[0029]FIG. 12 is a cross-sectional assembly view of the sole of FIG. 10;

[0030]FIG. 13 is a top view of the printed circuit depicted in FIGS.10-12;

[0031]FIG. 14 is a cross-sectional exploded assembly view of the printedcircuit of FIG. 13 taken along line 14-14 in FIG. 13; and

[0032]FIG. 15 is a side elevational view of the printed circuit of FIGS.10-14.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Referring now to the drawings for the purpose of illustrating theinvention and not for the purpose of limiting the same, FIG. 1illustrates an embodiment of the present invention in the form of anitem of footwear 10 employing an embodiment of a flexible printedcircuit 100 of the present invention. As the present DetailedDescription of the Invention proceeds, those of ordinary skill in theart will appreciate that the flexible printed circuits 100 may be usedin combination with a variety of different types of footwear withoutdeparting from the spirit and scope of the present invention. Thus, theprotection afforded to the various embodiments of the present inventionshould not be limited to footwear having the specific cross-sectionalshape and configuration depicted in FIG. 1.

[0034] As can be seen in FIG. 1, the item of footwear 10 includes anupper 20 that may be fabricated from a variety of materials such ascanvas, leather, etc. The upper 20 may be attached to the sole assembly30 by conventional footwear assembly processes and techniques. In thisembodiment, the sole assembly 30 includes an electrically conductiveoutsole 40, a non-electrically conductive midsole 50, an electricallyconductive insole 70 and an electrically conductive sock liner 80. Inaddition, as will be described in further detail below, a flexiblecircuit 100 is supported within the midsole 50 to define at least oneelectrically conductive path having a desired impedance that extendsbetween the electrically conductive insole board 70 and the electricallyconductive outsole 40. As used herein, the term “electricallyconductive” refers to the ability to transmit an electrical currenttherethrough.

[0035] In this embodiment, the outsole 40 may be fabricated from apolyurethane or similar rubber material that is mixed with carbon powderutilizing known fabrication techniques and processes such that theoutsole 40 will conduct an electrical current. In one embodiment, it isdesirable for the outsole 40 to have a resistance value of less than1×10⁶ ohms. However, the outsole 40 could conceivably be fabricated fromother materials having similar electrically conductive characteristics.As can be seen in FIGS. 1 and 3, the outsole 40 has an upper surface 42and a lower surface 44 that may have a tread pattern 46 formed thereon.

[0036] The midsole 50 of this embodiment may be fabricated from anon-conductive material such as polyurethane or EVA. As used herein, theterm “non-conductive” means having an electrical impedance value that isgreater than 1×10⁷ ohms. However, the midsole 50 may be fabricated fromother suitable materials that essentially do not conduct electricalcurrent. In one embodiment, the midsole 50 has a resistance that isgreater than 1×10⁷ ohms. As can be seen in FIGS. 3 and 4, a cavity 52 isprovided through the midsole 50 to enable the printed circuit 100 toextend therethrough and thereby be supported by the midsole 50 as willbe discussed in further detail below. Also in this embodiment, theinsole 70 and the conductive sock liner 80 may be fabricated frompolyurethane or similar material that contains a carbon powder toprovide these elements with the ability to conduct an electricalcurrent. Also in this embodiment, the insole 70 and the sock liner 80have a resistance value that is less than 1×10⁶ ohms. Thus, in thisembodiment, the outsole 40 has an electrical impedance, the midsole 50has an electrical impedance that is greater than the electricalimpedance of the outsole 40, and the insole 70 has an electricalimpedance that is less than the electrical impedance of the midsole.

[0037] One embodiment of a printed circuit 100 of the present inventionis depicted in FIGS. 5-9. In this embodiment, the printed circuit 100includes at least one electrically conductive path or conductor path. Ascan be seen in FIGS. 5 and 6, this embodiment of the printed circuit 100includes a first electrically conductive path 110, a second electricallyconductive path 120 and a third electrically conductive path 130. Thepaths 110, 120, 130 may be formed from copper foil or similar materialutilizing conventional chemical milling techniques. In this embodiment,the electrical conductive paths 110, 120, 130 may be approximately 251μm thick. However, copper foil or similar materials having otherthicknesses could conceivably be used.

[0038] The electrically conductive paths 110, 120, 130 may be attachedto a first substrate 140 with a commercially available adhesive 149 suchas that adhesive supplied by King Her Chemical Industrial Corporation ofNo. 38, 18^(th) RD., Industrial Park, Taichung, Taiwan, R.O.C. However,other similar adhesives may be employed. In this embodiment, the firstsubstrate may comprise a polyimide sheet material and having a thicknessof 18 μm. However, other flexible sheet materials may also be used. Thefirst substrate has a first end 142 and a second end 144 and a firstside 146 and a second side 148. The first electrically conductive path110, the second electrically conductive path 120 and the thirdelectrically conductive path 130 are attached to the first side 146 ofthe first substrate 140 such that a first end 112 of the first path 110is adjacent the first end 142 of the first substrate and the second end114 of the first path 110 is adjacent the second end of the firstsubstrate, the first end 122 of the second path is adjacent the firstend 142 of the first substrate 140, the second end 124 of the secondpath 120 is adjacent the second end 144 of the first substrate 140, thefirst end 132 of the third path 130 is adjacent to the first end 142 ofthe first substrate 140 and the second end 134 of the third path 130 isadjacent to the second end 144 of the first substrate 140. See FIGS. 5and 7. The paths 110, 120, 130 may be attached to the first side of 146of the first substrate 140 by a layer of commercially available adhesive149, such as that adhesive described above.

[0039] Also in this embodiment, a first resistor 116 is electricallycoupled to the first path 110. A second resistor 126 is electricallycoupled to the second path 120. A third resistor 136 is electricallycoupled to the third path 130. The resistors 116, 126, 136 may comprisecommercially available 6.8M-ohm resistors that extend through the firstsubstrate 140 and are electrically coupled (soldered, etc.) to theirrespective path. In this embodiment, second substrate 150, in the formof polyimide sheet may be attached to the first side 146 of the firstsubstrate and the central portions 118, 128, 138 of the first, secondand third paths 110, 120, 130, respectively by a second layer ofcommercially available adhesive 151 of the type described above. Inparticular, the central portion 118 of the first path, the centralportion 128 of the second path 120 and the central portion 138 of thethird path are encapsulated between the first substrate 140 and thesecond substrate 150. As can be seen in FIGS. 5 and 7, the secondsubstrate only covers the central portions of the paths such that thefirst ends 112, 122, 132, of the first, second and third paths 110, 120,130, respectively are exposed. See FIG. 7. In this embodiment, theprinted circuit 100 is assembled under pressure and may have an overallthickness of approximately 80-90 μm. An overall thickness of less than 3mm should also work well. However, the printed circuit 100 may have avariety of other thicknesses that afford the circuit 100 the flexibilityto be positioned within the sole assembly 30 as will be furtherdiscussed below. Thus, as used herein, the term “flexible” means that atleast one portion of the circuit 100 may be bent or positioned relativeto another position of the printed circuit such that those portions arenot coplanar with respect to each other without damaging the printedcircuit or its components (i.e., without hampering or destroying theability of the first, second and third paths 110, 120, 130, respectivelyto conduct electrical current). The skilled artisan will appreciate thatsuch construction enables the flexible printed circuit to be installedin a variety of advantageous configurations. It is conceivable, however,that the conductive paths 110, 120, 130, etc. may be affixed to arelatively rigid substrate that that has been preformed to a desiredshape for installation in the manner described herein. Therefore, whilethe flexible substrates and circuits described herein are capable offlexing with the sole, it is conceivable that rigid substrates couldalso be employed. Thus, the protection afforded to the printed circuitherein should not be limited to circuits formed on flexible substrates,but should also encompass rigid printed circuits.

[0040] As was described above, the flexible printed circuit 100 isprovided with three paths or conductors 110, 120, 130 that have acorresponding resistor 116, 126, 136 attached thereto. The total amountof resistance through the flexible printed circuit 100 is determined bythe quantity and size of resistors employed. For example, the totalimpedance for the three 6.8M ohm resistors may be calculated as follows:$\frac{{R1} \times {R2} \times {R3}}{{{R1} \times {R2}} + {{R1} \times {R3}} + {{R2} \times {R3}}} = {{2.267\quad M\quad {ohms}} = {2.267 \times 10^{6}\quad {{ohms}.}}}$

[0041] If one of the three resistors fails, the total impedance valuefor the flexible circuit board of this embodiment will be:$\frac{{R1} \times {R2}}{{R1} + {R2}} = {{3.4\quad M\quad {ohms}} = {3.4 \times 10^{6}\quad {{ohms}.}}}$

[0042] As indicated above, at least one major company in the computerindustry recommends that the impedance of a conductive shoe bemaintained within 10⁶ ohms to 10⁷ ohms. Thus, in this embodiment, evenif two resistors fail, the total impedance value will be at 6.8×10⁶ohms, which is still below the upper limit of 10 ⁷ ohms.

[0043] Those of ordinary skill in the art will appreciate that theimpedance of the flexible circuit board may be varied by altering thenumber of paths (conductors) and resistors to achieve a desired amountof impedance in accordance with standard electrical engineering formulas(i.e., “Ohm's Law”). For example, series arrays or combination arraysmay be used and their total impedance may be calculated as follows:

[0044] One Resistor:

R(total resistance value)=R1

[0045] Two Resistors (Combination Arrays):${R\quad \text{(total~~resistance~~value)}} = \frac{{R1} \times {R2}}{{R1} + {R2}}$

[0046] Three Resistors (Combination Arrays):${R\text{(total~~resistance~~value)}} = \frac{{R1} \times {R2} \times {R3}}{{{R1} \times {R2}} + {{R1} \times {R3}} + {{R2} \times {R3}}}$

[0047] Series Arrays:

R(total resistance value)=R1+R2+R3+ . . .

[0048] In this embodiment, a moisture resistant barrier 180 may bewrapped over the resistors 116, 126, 136 to retard and prevent theinfiltration of moisture into the points where the resistors 116, 126,136 are coupled to the paths 110, 120, 130, respectively. The moisturebarrier 180 may comprise a wrapping of conventional electricalinsulation tape. However, the moisture resistant barrier 180 may beformed with other materials such as sealant, glue or the like.

[0049] The flexible printed circuit 100 may be installed in the footwearas shown in FIGS. 1, 2, 3 and 4. As can be seen in FIGS. 2 and 4, themidsole 50 has a hole or passageway 52 therethrough sized to receive aportion of the flexible circuit 100. In addition, an undercut 58 areamay be provided in the bottom surface 57 of the midsole 50 toaccommodate the resistors 116, 126, 136 when the circuit 100 issupported in the midsole 50 as shown. See FIG. 2. As can be seen, sucharrangement permits the circuit 100 to be oriented such that the firstend 112 of the first path 110, the second end 122 of the second path 120and the third end 132 of the third path 130 to be in electrical contactwith the conductive outsole 40 to transmit electrical current thereto.Similarly, the second end 114 of the first path 110 and the second end124 of the second path 120 and the second end 134 of the third path 130are supported in electrical contact with the conductive insole board 70to receive electrical current therefrom. If desired, the first end 142of the circuit 100 may be attached to the underside 57 of the midsolewith double-sided adhesive tape 159 or other commercially availableconductive adhesive. A variety of different types of adhesives oradhesive tapes may be used. For example, the double-sided tapemanufactured by the 3M Company under Model No. 467 may be employed.Similarly, the second end 144 of the circuit 100 may be affixed to theupper surface 59 of the midsole by another section of such double-sidedadhesive tape 159 or other commercially available adhesive. The readerwill appreciate that when the flexible circuit 100 is installed as shownin FIGS. 1, 2, 3, and 4, the exposed ends 112, 122, 132, of the paths110, 120, 130, respectively remain exposed to contact the conductiveoutsole 40 and the exposed ends 114, 124, 134 of the paths 110, 120,130, respectively are exposed to contact the conductive insole board 70.In this embodiment, the end 142 of the flexible circuit 100 thatcontains the exposed ends 112, 122, 132 may be fastened to the outsole40 with commercially available ESD conductor glue 170 that has aresistance range of 5×10⁴˜10⁶ Ohms. The midsole 50 is attached to theoutsole 40 by commercially available conductive cement. Similarly, theinsole board 70 is attached to the midsole 50 by commercially availableconductive cement. In this embodiment, the sock liner is not attached tothe insole board. Thus, when installed as shown in FIGS. 1 and 2, theexposed ends 114, 124, 134 of the paths 110, 120, 130, respectivelycontact the conductive insole board 70 and the flexible circuit 100extends through the opening 52 in the midsole 50 and the exposed ends112, 122, 124 of the paths 110, 120, 130, respectively, contact theconductive outsole 40. Therefore, such arrangement permits a staticcharge to pass from the foot through the conductive sock liner 80,through the conductive insole board 70, through the paths 110, 120, 130and resistors 116, 126, 136 to provide an impedance of 2.267×10⁶ ohms.This charge then passes from the paths 110, 120, 130 to the conductiveoutsole 40 such that the charge is safely dissipated to the floorsurface. In this embodiment, by way of example only, the impedance ofthe respective parts of the sole assembly is: sock liner 80:2.5×10⁴-2×10⁵ ohms; insole board 70: 10⁴-10⁵ ohms; resistors 116, 126,136: 6.8×10⁶ ohms (each); midsole 50: 10¹¹-10¹² ohms; conductive outsole40: 10⁴-3×10⁴ ohms; and conductive adhesive: 10⁴-10⁵ ohms.

[0050] To test the effectiveness of the above-mentioned design, twodifferent items of footwear manufactured in accordance with theabove-mentioned embodiment of the present invention were tested asoutlined below by Fowler Associates, Inc. of 3551 Moore-Duncan Highway,Moore, S.C. 29639:

[0051] Iron Age® Women's Style 492M, SIZE 7M Steel Toe Hiker

[0052] Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2

[0053] Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc,100 vdc, 500 vdc

[0054] Electrodes: 2½ in. aluminum cylinder, aluminum plate, aluminumfoil

[0055] Laboratory conditions: 73° F., 12% RH Resistance of Individual toGround - Ohms Laboratory conditions: 73° F., 12% After 3 mins. of WearAfter 5 mins. of Wear Test Sample 10 v 100 v 10 v 100 v Style 492M Both2.69 × 10⁶ 1.83 × 10⁶ 2.50 × 10⁶ 1.73 × 10⁶ Left 4.23 × 10⁶ 3.18 × 10⁶4.15 × 10⁶ 3.13 × 10⁶ Right 4.43 × 10⁶ 3.41 × 10⁶ 4.23 × 10⁶ 3.35 × 10⁶Resistance of Shoe to Ground per ESD S9.1 - Ohms 25 lbs. lead shot inShoe Test Sample 100 v Style 492M Left 4.17 × 10⁶ Right 4.81 × 10⁶

[0056] **These tests are in general agreement with ANSI Z41-1999 andaccording to ESD S9.1 and DSTM 54.2. ANSI-Z41 states 50% RH and voltagebetween 25 volts and 50 volts. These tests were performed at 10 voltsand 100 volts at 12% RH. These conditions are more stringent than ANSIZ41.

[0057] Iron Age® Women's Style 492M, SIZE 6M Steel Toe Hiker

[0058] Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2

[0059] Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc,100 vdc, 500 vdc

[0060] Electrodes: 2½ in. aluminum cylinder, aluminum plate, aluminumfoil

[0061] Laboratory conditions: 73° F., 12% RH Resistance of Individual toGround - Ohms Laboratory conditions: 73° F., 12% After 3 mins. Of WearAfter 5 mins. of Wear Test Sample 10 v 100 v 10 v 100 v Style 492M Both2.32 × 10⁶ 1.44 × 10⁶ 2.21 × 10⁶ 1.47 × 10⁶ Left 3.86 × 10⁶ 2.80 × 10⁶3.87 × 10⁶ 2.88 × 10⁶ Right 3.49 × 10⁶ 2.56 × 10⁶ 3.40 × 10⁶ 2.55 × 10⁶Resistance of Shoe to Ground per ESD S9.1 - Ohms 25 lbs. lead shot inShoe Test Sample 100 v Style 492M Left 4.12 × 10⁶ Right 3.01 × 10⁶

[0062] **These tests are in general agreement with ANSI Z41-1999 andaccording to ESD S9.1 and DSTM 54.2. ANSI-Z41 states 50% RH and voltagebetween 25 volts and 50 volts. These tests were performed at 10 voltsand 100 volts at 12% RH. These conditions are more stringent than ANSIZ41.

[0063] Iron Age® Women's Style 492M, SIZE 6M Steel Toe Hiker

[0064] Test Methods: ANSI Z41-1999**, ESD S 9.1 and ESD DSTM 54.2

[0065] Test Equipment: Dr. Thiedig MegOhm Meter Applied voltage: 10 vdc,100 vdc, 500 vdc

[0066] Electrodes: 2½ V₂ in. aluminum cylinder, aluminum plate, aluminumfoil

[0067] Laboratory conditions: 73° F., 12% RH Resistance of Individual toGround - Ohms Laboratory conditions: 73° F., 50% After 3 mins. Of WearAfter 5 mins. of Wear Test Sample 10 v 100 v 10 v 100 v Style 492M Both3.48 × 10⁶ 1.50 × 10⁶ 3.25 × 10⁶ 1.60 × 10⁶ Left 5.16 × 10⁶ 2.84 × 10⁶4.22 × 10⁶ 3.05 × 10⁶ Right 5.26 × 10⁶ 2.90 × 10⁶ 4.05 × 10⁶ 2.96 × 10⁶Resistance of Shoe to Ground per ESD S9.1 - Ohms 25 lbs. lead shot inShoe Test Sample 100 v Style 492M Left 3.21 × 10⁶ Right 2.78 × 10⁶

[0068] **These tests are in general agreement with ANSI Z41-1999 andaccording to ESD S9.1 and DSTM 54.2. ANSI-Z41 states 50% RH and voltagebetween 25 volts and 50 volts. These tests were performed at 10 voltsand 100 volts at 12% RH. These conditions are more stringent than ANSIZ41.

[0069] As can be appreciated from the foregoing description, the variousembodiments of the present invention represent a vast improvement overprior footwear designs that are constructed to dissipate staticelectricity. In particular, the flexible circuit board embodiments ofthe present invention are relatively compact and require minimal spaceto install. Furthermore, because they are flexible, they are not assusceptible to damage as the conventional resistors used in other shoedesigns. The resistors provide a series of load bearing contact surfacesfor more uniform distribution of the weight pressure from the insole tothe outsole, and thus result in reduction of the pressure in eachresistor. The impendence dimensions of the resistors employed by thepresent invention are generally smaller and more stable than such priorresistor arrangements and, therefore, they can typically resist morepressure. Furthermore, if one or two of the resistors of the presentinvention fail, the total impedance value will be below 10⁷ ohms.Furthermore, because the flexible circuit board determines the majorpart of the impedance of the sole, the impendence of the sole materialsemployed is less critical. Therefore a wider range of materials can beused to fabricate the sole. Manufacturing costs can thus be greatlyreduced without affecting quality requirement because the impedance ofthe resistor components in the midsole is very stable and will notchange in a wet environment such as perspiration from the wearer's footor a wet floor surface, the total impedance of the sole can still bemaintained within a desired range of impedance.

[0070] Another printed circuit 200 embodiment of the present inventionis depicted in FIGS. 10-15. In this embodiment, the printed circuit 200includes at least one electrically conductive path or conductor path. Ascan be seen in FIG. 12, this embodiment of the printed circuit 200includes a first electrically conductive path 210, a second electricallyconductive path 220 and a third electrically conductive path 230. Thepaths 210, 220, 230 may be formed from copper foil or similar materialutilizing conventional chemical milling techniques. In this embodiment,the electrical conductive paths 210, 220, 230 may be approximately 25 μmthick. However, copper foil or similar materials having otherthicknesses could conceivably be used.

[0071] The electrically conductive paths 210, 220, 230 may be attachedto a first substrate 240 with a commercially available adhesive 249 suchas that adhesive supplied by King Her Chemical Industrial Corporation ofNo. 38, 18^(th) RD., Industrial Park, Taichung, Taiwan, R.O.C. However,other similar adhesives may be employed. See FIG. 13. In thisembodiment, the first substrate 240 may comprise a polyimide sheetmaterial and having a thickness of 18 μm. However, other flexible sheetmaterials may also be used. The first substrate 240 has a first end 242and a second end 244 and a first side 246 and a second side 248. Thefirst electrically conductive path 210, the second electricallyconductive path 220 and the third electrically conductive path 230 areattached to the first side 246 of the first substrate 240 such that afirst end 212 of the first path 210 is adjacent the first end 242 of thefirst substrate and the second end 214 of the first path 210 is adjacentthe second end 244 of the first substrate 240, the first end 222 of thesecond path is adjacent the first end 242 of the first substrate 240,the second end 224 of the second path 220 is adjacent the second end 244of the first substrate 240, the first end 232 of the third path 230 isadjacent to the first end 242 of the first substrate 240 and the secondend 234 of the third path 230 is adjacent to the second end 244 of thefirst substrate 240. See FIGS. 12 and 13. The paths 210, 220, 230 may beattached to the first side of 246 of the first substrate 240 by a layerof commercially available adhesive 249, such as that adhesive such asthat adhesive supplied by King Her Chemical Industrial Corporation ofNo. 38, 18^(th) RD., Industrial Park, Taichung, Taiwan, R.O.C. However,other similar adhesives may be employed.

[0072] Also in this embodiment, a first resistor 216 is electricallycoupled to the first path 210. A second resistor 226 is electricallycoupled to the second path 220. A third resistor 236 is electricallycoupled to the third path 230. The resistors 216, 226, 236 may comprisecommercially available 6.8M-ohm resistors that are electrically coupled(soldered, etc.) to their respective path. In this embodiment, a secondsubstrate 250, in the form of polyimide sheet may be attached to thefirst side 246 of the first substrate and the central portions 218, 228,238 of the first, second and third paths 210, 220, 230, respectively bya second layer of commercially available adhesive 251 of the typedescribed above. In particular, the central portion 218 of the firstpath 210, the central portion 228 of the second path 220 and the centralportion 238 of the third path 230 are encapsulated between the firstsubstrate 240 and the second substrate 250. As can be seen in FIG. 13,the second substrate 250 only covers the central portions of the pathssuch that the first ends 212, 222, 232, of the first, second and thirdpaths 210, 220, 230, respectively are exposed.

[0073] In this embodiment, the printed circuit 200 is assembled underpressure and may have an overall thickness of approximately 80-90 μm. Anoverall thickness of less than 3 mm should also work well. However, theprinted circuit 200 may have a variety of other thicknesses that affordthe circuit 200 the flexibility to be positioned within the soleassembly 30 as will be further discussed below. Thus, as used herein,the term “flexible” means that at least one portion of the circuit 200may be bent or positioned relative to another position of the printedcircuit such that those portions are not coplanar with respect to eachother without damaging the printed circuit or its components (i.e.,without hampering or destroying the ability of the first, second andthird paths 210, 220, 230, respectively to conduct electrical current).The skilled artisan will appreciate that such construction enables theflexible printed circuit to be installed in a variety of advantageousconfigurations. It is conceivable, however, that the conductive paths210, 220, 230, etc. may be affixed to a relatively rigid substrate thatthat has been preformed to a desired shape for installation in themanner described herein. Therefore, while the flexible substrates andcircuits described herein are capable of flexing with the sole, it isconceivable that rigid substrates could also be employed. Thus, theprotection afforded to the printed circuit herein should not be limitedto circuits formed on flexible substrates, but should also encompassrigid printed circuits.

[0074] Also in this embodiment, a first attachment pad assembly 300 isattached to a first end 290 of the printed circuit 200 and a second padassembly 320 is attached to a second end 292 of the printed circuit 200.Such attachment pad assemblies provide an increased area foraccommodating adhesive for attaching the ends of the printed circuit toportions of the sole assembly. More specifically and with reference toFIGS. 12-14, the first pad assembly 300 of this embodiment may comprise,for example, a first pad member 302 and a primary pad member 304. Inthis embodiment, the first and primary pad members 302, 304 arefabricated from a commercially available conductive EVA material.However, other conductive materials may be employed. In this embodiment,the first and primary pad members 302, 304 afford a relatively largearea for attachment to the other sole components as will be discussed infurther detail below. For example, the first and primary pad members302, 304 may be approximately 1.5 inches (38 mm)×approximately 1.25inches (31.75 mm) and 0.0625 inches (1.6 mm) thick. However, it isconceivable that the first and primary pad members 302, 304 may be madein other suitable sizes and that the sizes of the first and primary padmembers 302, 304 may be dissimilar.

[0075] The first ends 212, 222, 232 of the conductive pathways 210, 220,230, respectively may be affixed to the first pad member 302 by aconductive adhesive 306 of the type described above. Similarly, aportion of the first substrate 240 may be attached to the primary padmember by another layer of the conductive adhesive 306. The conductiveadhesive 306 may also serve to join the first pad member 302 to theprimary pad member 304. In addition, the first ends 212, 222, 232 of theconductive pathways 210, 220, 230, respectively may be joined to thefirst and primary pad members 302, 304 by stitches 310 which extendthrough the first end of the printed circuit 200 and the first andprimary pad members 302, 304. The stitches 310 may be formed from aconductive or non-conductive thread or similar material.

[0076] Likewise, the second pad assembly 320 of this embodiment maycomprise, for example, a second pad member 322 and a secondary padmember 324. In this embodiment, the second and secondary pad members322, 324 may also be fabricated from conductive EVA material. The secondand secondary pad assemblies afford a relatively large area forattachment to the other sole components as will be discussed in furtherdetail below. For example, the second and secondary pad members may beapproximately 1.5 inches (38 mm)×approximately 1.25 inches (31.75 mm)and 0.0625 (1.6 mm) thick. However, it is conceivable that the secondand secondary pad members 322, 324 may be made in other suitable sizesand that the sizes of the second and secondary pad members 322, 324 maybe dissimilar.

[0077] The second ends 212, 222, 232 of the conductive pathways 210,220, 230, respectively may be affixed to the second pad member 322 by aconductive adhesive 306 of the type described above. Similarly, the end244 of the first substrate 240 may be attached to the secondary padmember 324 by another layer of the conductive adhesive 306. Theconductive adhesive 306 may also serve to join the second pad member 322to the secondary pad member 324. In addition, the first ends 212, 222,232 of the conductive pathways 210, 220, 230, respectively may be joinedto the second and secondary pad members 322, 324 by stitches 330 whichextend through the second end 292 of the printed circuit 200 and thesecond and secondary pad members 322, 324. The stitches 330 may beformed from conductive or non-conductive thread or similar material.

[0078] As was described above, the flexible printed circuit 200 isprovided with three paths or conductors 210, 220, 230 that have acorresponding resistor 216, 226, 236 attached thereto. The total amountof resistance through the flexible printed circuit 200 is determined bythe quantity and size of resistors employed. For example, the totalimpedance for the three 6.8M ohm resistors may be calculated as setforth above and may equal 2.267 M ohms=2.267×10⁶ ohms. If one of thethree resistors fails, the total impedance value for the flexiblecircuit board of this embodiment will be 3.4 M ohms=3.4×10⁶ ohms. Asindicated above, at least one major company in the computer industryrecommends that the impedance of a conductive shoe be maintained within10⁶ ohms to 10⁷ ohms. Thus, in this embodiment, even if two resistorsfail, the total impedance value will be at 6.8×10⁶ ohms, which is stillbelow the upper limit of 10⁷ ohms.

[0079] Those of ordinary skill in the art will appreciate that theimpedance of the flexible circuit board 200 may be varied by alteringthe number of paths (conductors) and resistors to achieve a desiredamount of impedance in accordance with standard electrical engineeringformulas (i.e., “Ohm's Law”) that were set forth above. In thisembodiment, a moisture resistant barrier 280 may be wrapped over theresistors 216, 226, 236 to retard and prevent the infiltration ofmoisture into the points where the resistors 216, 226, 236 are coupledto the paths 210, 220, 230, respectively. The moisture barrier 280 maycomprise a wrapping of conventional electrical insulation tape. However,the moisture resistant barrier 280 may be formed with other materialssuch as sealant, glue or the like.

[0080] The flexible printed circuit 200 may be installed in the footwearas shown in FIGS. 10 and 11. As can be seen in those Figures, themidsole 50 has a hole or passageway 52 therethrough sized to receive aportion of the flexible circuit 200. In addition, an undercut 58 areamay be provided in the bottom surface 57 of the midsole 50 toaccommodate the resistors 216, 226, 236 and the first pad assembly 320when the circuit 200 is supported in the midsole 50 as shown. Likewise,an upper notch 58′ may be provided in the upper surface 59 of themidsole 50 to accommodate the second pad assembly 320. See FIG. 12. Ascan be seen, such arrangement permits the circuit 200 to be orientedsuch that the first pad assembly 302 is in electrical contact with theconductive outsole 40 to transmit electrical current thereto. Similarly,the second pad assembly 320 is supported in electrical contact with theconductive insole board 70 to receive electrical current therefrom. Ifdesired, the first pad assembly may be attached to the underside 57 ofthe midsole with a conductive adhesive such as a commercially availableESD conductor glue 170 that has a resistance range of 5×10⁴˜10⁶ Ohms orother similar glues or adhesive mediums. Similarly, the second padassembly 320 may be affixed to the upper surface 59 of the midsole byanother such conductive adhesive. The midsole 50 is attached to theoutsole 40 by commercially available conductive cement. Similarly, theinsole board 70 is attached to the midsole 50 by commercially availableconductive cement. In this embodiment, the sock liner 80 is not attachedto the insole board. Thus, when installed as shown in FIGS. 10 and 11,the second conductive pad assembly 320 is affixed to the conductiveinsole board 70 and the flexible circuit 200 extends through the opening52 in the midsole 50 and the first conductive pad assembly 300 isattached to the conductive outsole 40. Therefore, such arrangementpermits a static charge to pass from the foot through the conductivesock liner 80, through the conductive insole board 70, through thesecond conductive pad assembly 320, through paths 210, 220, 230 andresistors 216, 226, 236 to provide an impedance of 2.267×10⁶ ohms. Thischarge then passes from the paths 210, 220, 230 through the firstconductive pad assembly 300 to the conductive outsole 40 such that thecharge is safely dissipated to the floor surface. In this embodiment, byway of example only, the impedance of the respective parts of the soleassembly is: sock liner 80: 2.5×10⁴-2×10⁵ ohms; insole board 70: 10⁴-10⁵ohms; resistors 116, 126, 136: 6.8×10⁶ ohms (each); midsole 50:10¹¹-10¹² ohms; conductive outsole 40: 10⁴-3×10⁴ ohms; and conductiveadhesive: 10⁴-10⁵ ohms. This embodiment would also have results similarto those test results set forth above.

[0081] As can be appreciated from the foregoing description, the variousembodiments of the present invention represent a vast improvement overprior footwear designs that are constructed to dissipate staticelectricity. In particular, the flexible circuit board embodiments ofthe present invention are relatively compact and require minimal spaceto install. Furthermore, because they are flexible, they are not assusceptible to damage as the conventional resistors used in other shoedesigns. The resistors provide a series of load bearing contact surfacesfor more uniform distribution of the weight pressure from the insole tothe outsole, and thus result in reduction of the pressure in eachresistor. The impendence dimensions of the resistors employed by thepresent invention are generally smaller and more stable than such priorresistor arrangements and, therefore, they can typically resist morepressure. Furthermore, if one or two of the resistors of the presentinvention fail, the total impedance value will be below 10⁷ ohms.Furthermore, because the flexible circuit board determines the majorpart of the impedance of the sole, the impendence of the sole materialsemployed is less critical. Therefore a wider range of materials can beused to fabricate the sole. Manufacturing costs can thus be greatlyreduced without affecting quality requirement because the impedance ofthe resistor components in the midsole is very stable and will notchange in a wet environment such as perspiration from the wearer's footor a wet floor surface, the total impedance of the sole can still bemaintained within a desired range of impedance.

[0082] Whereas particular embodiments of the invention have beendescribed herein for the purpose of illustrating the invention and notfor the purpose of limiting the same, it will be appreciated by those ofordinary skill in the art that numerous variations of the details,materials and arrangement of parts may be made within the principle andscope of the invention without departing from the invention as describedin the appended claims.

What is claimed is:
 1. An electrostatic circuit for a sole having an outsole, an insole and a midsole positioned between the insole and outsole, said electrostatic circuit comprising: a first substrate having a first end and a second end; at least one conductor path attached to said first substrate, each said conductor path having a first exposed end adjacent said first end of said first substrate and being attachable to the outsole and a second exposed end adjacent said second end of said substrate and attachable to the insole; and at least one resistor electrically coupled to each said conductor path and mounted to said first substrate. 